Question about how my open center FEL valve with power beyond

[etpm]

Hi All,
I was wondering how this works. I understand the open center. When the valve is operating a pair of cylinders the fluid goes to the cylinders. When the valve is back at the neutral position the fluid is vented to the port that goes back to the reservoir. I don't understand how the power beyond function works. I know it delivers fluid under pressure to stuff downstream, in my case the 3PH. But why not just use the port that goes to the reservoir? The 3PH valve is also open center. At least I think it is from reading the manual. The tractor is a Yanmar YM2310 and the FEL is aftermarket. I looked at the plumbing and from the FEL valve there is a port supplying fluid to the 3PH and another that goes to the reservoir.
Thanks,
Eric

 

[oldnslo]

Two reason to not use tank line to reservoir as power beyond.
1) most cast valves the tank core is only rated for low pressure like 250 PSI or less. Higher pressure can crack the casting and or blow out the seals on the spools.
2) any back pressure in the tank line directly reduces the amount of pressure available for work.
As an Example:at 3000 PSI a loader will lift 3000 lbs. 1,000 PSI back pressure in tank port and now you only have 2,000 PSI available so can only lift 2,000 lbs.

Power beyond allows full system pressure to be used down stream with out damage to the valve.

 

[wdchyd]

Having two control valves in series without PB circuit makes problems.
The orings on the spools in valve number one will directly see any backpressure downstream resulting in premature oring failure.
And if both control valves in series are operated to max relief pressure the pressure is additive. The first valve will see both pressures added together……..Boooom.

 

[etpm]

Two reason to not use tank line to reservoir as power beyond.
1) most cast valves the tank core is only rated for low pressure like 250 PSI or less. Higher pressure can crack the casting and or blow out the seals on the spools.
2) any back pressure in the tank line directly reduces the amount of pressure available for work.
As an Example:at 3000 PSI a loader will lift 3000 lbs. 1,000 PSI back pressure in tank port and now you only have 2,000 PSI available so can only lift 2,000 lbs.

Power beyond allows full system pressure to be used down stream with out damage to the valve.

Thanks for the reply old guy. So this probably means that the tank port is shut off when the power beyond port is being used.
Thanks,
Eric

 

[etpm]

Having two control valves in series without PB circuit makes problems.
The orings on the spools in valve number one will directly see any backpressure downstream resulting in premature oring failure.
And if both control valves in series are operated to max relief pressure the pressure is additive. The first valve will see both pressures added together……..Boooom.

I can see how that would be very bad.
Thanks,
Eric

 

[wdchyd]

Just to show this came from a Vickers training manual. Same principle of multiple resistance in series valves.

 

[wdchyd]

 

[oldnslo]

Thanks for the reply old guy. So this probably means that the tank port is shut off when the power beyond port is being used.
Thanks,
Eric

Correct, The tank port is not connected to the power beyond port. Note: for the valve to work properly the power beyond port must be open to tank when all valves are in neutral position and tank port must be connected directly to tank.

 

[LD1]

Power beyond is where the fluid normally flows when the valve isnt being used.

The tank/return gives a place for fluid to go when USING the valve. So when you use the loader valve......you are pushing fluid to one side of the cylinder and expelling the fluid out of the other side of the cylinder right? This returns via the tank port straight back to tank.

Have seen many threads on here where a FEL or 3PH is acting strange and it's a homebrew install without the PB on the loader.

 

[npalen]

I'm trying to understand how the diagram and video above apply to this thread topic. I don't think that the directional valves in a series have check valves working when all the spools are centered. (ie not being used) The leading valve must have a pressure relief valve to protect the pump and each valve spool may have anti-drop check valves but they would not function the same as the check valves shown above. Right?